a) Field of the Invention
The present invention relates to a light source device which is to be employed for endoscopes such as fiber scopes, non-flexible endoscopes, video scopes and so
b) Description of the Prior Art
There is conventionally known a light source device which consists, as illustrated in FIG. 1, of a light source lamp 1, and an optical system composed of a reflecting mirror 2 and a collector lens component 3 for imaging or collecting a light bundle emitted from the light source lamp 1. This light source device is configured so as to allow the light bundle to be incident onto a light guide fiber bundle 4 which is disposed in an endoscope for transmitting an illuminating light bundle.
Most of light source lamps which are used in general light source devices are xenon lamps, halogen lamps and metal halide lamps. These lamps are ordinarily used in combination with reflecting mirrors which are disposed so as to have focal points thereof located at bright spots of the light source lamps and reflect light bundles in forms of parallel light bundles. Light bundles which are emitted from the light source lamps are divergent within certain angles which are determined dependently on sizes of the bright spots of the light source lamps and under influences due to rays emitted from the bright spots of the light source lamps, and have light intensity distributions such as that illustrated in FIG. 2. In this drawing, angles of emergence are taken as the abscissa and light intensities are taken as the ordinate. Further, the rays emitted from the light source lamps including those reflected by the reflecting mirrors are distributed with sufficient intensities within ranges of 4.degree. to 6.degree. at widest though the distributions of angles of the emerging rays are different dependently on types of the light source lamps. For this reason, the optical systems of the light source devices are adopted for collecting the rays emitted within the above-mentioned angles and leading there rays onto light guide fiber bundles. Since outside diameters of the endoscopes are restricted, restrictions are imposed also on outside diameters of the light guide fiber bundles. When real images of the bright spots of the light source lamps which are formed with the rays emitted from the light source lamps and having passed through the optical systems of the light source devices are not contracted sufficiently, intensities of the rays incident onto the light guide fiber bundles are low, thereby lowering utilizing efficiency of the rays emitted from the light source lamps.
As a conventional optical system for the light source devices for endoscopes which correct the defect described above, there is known, for example, an optical system disclosed by Japanese Patent Kokai Publication No. Hei 1-144,009. However, this optical system uses as many as four lens components, and therefore has a defect that it requires a high manufacturing cost and another defect that it has a complicated lens composition, thereby inevitably enlarging light source devices which comprise this optical system.